In the copending application referred to above it has been pointed out that the then-available electrical machining techniques, when applied to the forming of a 3D contour or surface pattern in a workpiece, commonly required a tool electrode three-dimensionally shaped to conform to the desired contour or surface pattern. Furthermore, a multiplicity of such solid electrodes of identical or similar configuration and size had to be prepared in order to compensate for the wear which the electrodes or tools suffered during the erosion process or in the interest of minimizing the machining time to obtain a desired machined precision and surface finish. Preparation of such precision-formed and multiple electrodes is obviously time-consuming and laborious.
In the copending application referred to above there is thus disclosed an electrical machining apparatus of a milling, sculpturing or shaving type for forming a 3D surface contour in a workpiece. The there disclosed apparatus comprises a wire or like continuous elongate electrode (hereinafter referred to as "wire" or "wire electrode"), a wire-advancing means for axially transporting the wire from a supply means to a takeup means, a workpiece support for carrying the workpiece, wire-guide means carried by a tool head and juxtaposed with the workpiece for positioning the wire transported under tension in a machining relationship with the workpiece, power supply means for electrically energizing the wire and the workpiece to electroerosively remove material from the latter across a fluid filled machining gap and machining feed means for relatively displacing the tool head and the workpiece support so as to cause the wire advanced over the guide means to sweep over a predetermined surface region on the workpiece along a predetermined machining path to form the 3D surface contour therein, the guide having an electrically nonconductive grooved wire-guiding surface for receiving the advancing wire so that it is substantially exposed to the juxtaposed workpiece surface.
The guide means may comprise one or more (e.g. a plurality of) guide members of rotary or non-rotary type whose wire guiding configuration may be adjustable to variably adjust the length, width and area of the wire running juxtaposed in a machining relationship with the workpiece surface.
The machining feed means may comprise first drive means for displacing the tool head toward and away from the workpiece along a Z-axis, second drive means for displacing the workpiece support in a plane along an X-axis and Y-axis which are orthogonal to each other and to the Z-axis. Preferably the feed means also includes third drive means comprising rotary means for rotating the tool head about the Z-axis so that the direction of traverse advance of the wire may always lie perpendicular to or, generally, a predetermined angle to, the surface being machined in the workpiece. In a typical shaving operation, the second and third drive means are used while milling and sculpturing operations generally require all of the first, second and third drive means to be operated in conjunction with one another. A conventional numerical controller may be used to operate the drive to cause the tool head to sweep over the workpiece surface under instructions of a program stored and preset to correspond to a desired sweeping path.
Additionally, fourth drive means may be incorporated to allow a tilt of the tool head with a variable angle relative to the workpiece so that the tool head and the workpiece are relatively displaced with five degrees of freedom.
It has also been pointed out that means is preferably provided additionally for imparting a high-frequency vibration in a sonic or ultrasonic range directly or indirectly, e.g. through a machining medium, to the wire advanced through the guide means in juxtaposition with the workpiece. The vibration may be provided by means of an electromechanical transducer or magnetostrictive element but, advantageously, may be induced in response to machining electrical pulses applied across the machining gap between the wire and the workpiece. Specifically, a resonant circuit is connected to the machining gap, whose resonant frequency is in tune with the frequency of the electrical oscillation generated at the machining gap.